1. Field of the Invention
The present invention relates to an improved structure of gold fingers and, more particularly, to an improved structure of gold fingers applied to a stacked-chip packaging structure.
2. Description of the Prior Art
The technique of multi-chip packaging, which involves the technique of stacking multiple chips and packaging them as an integrated circuit, has been widely adopted in the markets of memory packaging for mobile phones. FIG. 1 is a schematic diagram illustrating the structure of stacked-chip packaging. As shown in FIG. 1, a lower layer chip 12 and an upper layer chip 14 are provided on a packaging substrate 10. The lower layer chip 12 is bonded on the packaging substrate 10 by using a lower adhesive 16, whereas the upper layer chip 14 is bonded on the lower layer chip 12 by an upper adhesive 18. In addition, the lower layer chip 12 and the upper layer chip 14 are electrically connected to a gold finger 24 separately by means of a lower layer wire 22 and an upper layer wire 20 respectively.
Also, referring to FIG. 2, a groove 26 is set at the side of the lower adhesive 16 to impede outflow of the adhesive because it may flow along the packaging substrate 10. Nevertheless, the upper adhesive 18 can still flow along the lower layer wire 22 and eventually overflow all over the gold finger 24. If so, the upper layer wire 20 will have difficulty to perform wire bonding on the gold finger 24.
Moreover, as shown in FIG. 3, if the position of wire bonding from the lower layer wire 22 to the gold finger 24 is shifted, the upper layer wire 20 will also have difficulty to perform wire bonding on the gold finger 24 due to lack of enough space for doing it. Or the situation may be that the lower layer chip 12 is equal to or smaller than the upper layer chip 14 in size, as shown in FIG. 4. In such case, it will be even more difficult to reprocess wire bonding from the lower layer wire 22 to the gold finger 24 for solving the position shift problem.
In view of the above-mentioned problems encountered by the prior art, the present invention provides an improved structure of gold fingers to cope with the problems.